1. Field of the Invention
The present invention relates generally to a printing apparatus, and in particular relates to the control of discharging paper.
2. Description of the Background Art
Japanese Utility Model Published Application No. Sho 64-29343 discloses a printing apparatus comprising: a paper feed unit for feeding a sheet, a transportation unit for transporting the sheet fed from the paper feed unit to a predetermined location, a discharge unit for discharging the sheet transported from the transportation unit. The printing apparatus is provided with a detection unit for detecting the length of the sheet to be transferred to the discharge unit, a sensor for detecting the sheet received by the discharge unit, a discharge rotary unit for discharging the sheet detected by the sensor from the discharge unit, a control unit for reducing the rotation speed of the discharge rotary unit when the sheet is transported by the distance which is shorter than the distance corresponding to the length of the sheet after the sensor detects the leading edge of the sheet.
As described in this publication, it is a known technique that, in order not to roughly stack print sheets which are successively discharged to the catch tray of the printing apparatus, the transportation speed of the print sheets being discharged is reduced to a lower speed by decelerating a paper discharge roller unit when discharging the print sheets. By this configuration, it is possible to neatly arrange the stacked print sheet discharged onto the catch tray.
Generally speaking, there are a plurality of transfer roller units on the transportation route of the print sheet. Because of this, in a certain location of the transportation route, a print sheet is transported by a plurality of transfer roller units at the same time. Also, a print sheet is transferred between adjacent roller units. In this situation, if the roller unit near the catch tray is simply slowed down, there is a problem in that the print sheet is warped and deformed because of the differential speed between the roller units transporting the print sheet and that a loud hitting sound is caused when the print sheet comes in contact with the roller rotating at a different speed. Furthermore, the transportation speed before speed reduction varies depending on the printer option settings. Particularly, there is a substantial restriction on the transportation speed in the case of double-side printing which requires circulation of the print sheet in the housing of the printing apparatus. Because of this, the timing control of the speed reduction of the paper discharge roller unit cannot uniformly be made, but must be made by taking a variety of factors into consideration.